Thermal Treatment of Soybean Seeds can Improve the Quality of Soymilk by Enhancing the Extraction Efficiency of “Kokumi” Taste Components

Based on our recent finding that the “kokumi” taste components, γ-glutamyl-tyrosine, γ-glutamyl-phenylalanine, raffinose, and stachyose, are present in soybean seeds, we aimed to understand whether thermal treatment of soybean seeds can enhance the “kokumi” taste in soymilk or not. Heating was carried out prior to the grinding step in the soymilk production process. The extraction efficiency of the “kokumi” taste components changed with the type of thermal treatment. Autoclave and microwave heating of soybean seeds before grinding caused a high extraction efficiency of “kokumi” taste components compared to unheated and dry heat heating. Traditional methods, such as the thermal treatment at 90°C during grinding, also increased the “kokumi” taste components, but the efficiency and nitrogen yield were low compared to the thermal treatment before grinding. Enhanced extraction of “kokumi” taste components may be originated from the disruption of cell walls of soybean seeds induced by thermal treatment, and the degree of cell damage was closely related with the extraction efficiency of the “kokumi” taste components. Thus, instead of the traditional processes, the thermal treatment before grinding can contribute to the production of soymilk with greater “kokumi” taste components.